Water soluble hydroxyethyl methyl cellulose ether thickener for latex paint

ABSTRACT

NEW WATER-SOLUBLE HYDROXYETHYL METHYL CELLULOSE ETHERS HAVE BEEN PREPARED WHICH ARE IMPROVED THICKENERS FOR LATEX PAINT. THESE NEW ETHERS HAVE A THERMAL GEL POINT GREATER THAN 100*C., A HYDROXYETHYL MS OF ABOUT 1.0-3.5, A METHOXY DS OF ABOUT 0.6-1.6 AND A TOTAL DS OF ABOUT 1.4-2.4. LATEX PAINT THICKENED WITH THESE NEW ETHERS HAS IMPROVED ENZYME RESISTANCE AND COMPATIBILITY WITH PREDISPERSED COLORANTS.

United States Patent Oflice 3,709,876 Patented Jan. 9, 1973 U.S. Cl.260-231 A Claims ABSTRACT OF THE DISCLOSURE New water-solublehydroxyethyl methyl cellulose ethers have been prepared which areimproved thickeners for latex paint. These new ethers have a thermal gelpoint greater than 100 C., a hydroxyethyl MS of about 1.0-3.5, a methoxyD8 of about 0.6-1.6 and a total DS of about 1.4-2.4. Latex paintthickened with these new ethers has improved enzyme resistance andcompatibility with predispersed colorants.

BACKGROUND This application is a continuation-in-part of Ser. No.138,435 filed Apr. 29, 1971, now abandoned.

Water-soluble cellulose ethers have long been employed in aqueouscoating compositions as thickeners and protective colloids. Hydroxyethylcellulose products provide good flow and brush out with complete colordevelopment but have low resistance to bacterial degradation. Forexample, Lindenfors (Acta Chemica Scand, 16, 1111 (1962)) reports undercontrolled enzymatic hydrolysis conditions, a residual viscosity of 1.7%for hydroxyethyl cellulose with a molar substitution (MS) of 1.50compared with 3.8% for a methylhydroxyethyl cellulose (DS 1.66), 7.3%for methyl cellulose (DS 1.83) and 13.2% for a methylhydroxypropylcellulose (DS 1.9).

Rodgers, Wakeman, and Savage, U.S. 'Pat. 3,388,082 describes methylcellulose ethers with a high hydroxypropyl substitution which aresuitable thickeners with increased enzymatic resistance. Yet withcertain pigments, good color development and compatibility cannot beachieved with these hydroxypropyl ethers. By good color development ismeant the ability of a coating composition to retain a pigmentdispersion without significant loss of pigment effectiveness throughagglomeration of flocculation. It is visually evident in the coloruniformity of a coating applied with varying amount of shear.

By combining hydroxyethyl and methyl substitution in a new and carefullycontrolled manner, novel hydroxyethyl methyl cellulose ethers have beenprepared which have the complete color development characteristics of ahydroxyethyl cellulose plus the superior enzyme resistance of a methylcellulose, a combination highly desired for use as a latex paintthickener.

STATEMENT OF THE INVENTION The improved cellulose ether latex paintthickeners are water-soluble hydroxyethyl methyl cellulose ethers havinga thermal gel point greater than about 100 C., a hydroxyethyl molarsubstitution of about 1.0-3.5, a methoxyl degree of substitution ofabout 0.6-1.6, and a total degree of substitution of about 1.42.4 asfurther defined by the accompanying figure. To achieve the total degreeof substitution of about 1.4-2.4 requires a carefully controlledetherification of alkali cellulose with methyl chloride and ethyleneoxide. Preferably alkali cellulose, prepared by blending about 1.23.0moles NaOH per mole cellulose, is reacted with about 1.6-6.0 molesmethyl chloride and about 3.4-6.8 moles ethylene oxide at about 40-60 C.The new hydroxyethyl methyl cellulose products have a high resistance toenzymatic degradation and provide good color development andcompatibility when used as a latex paint thickener.

GENERAL DESCRIPTION The new hydroxyethyl methyl cellulose ethersdisclosed herein are ethers with a thermal gel point greater than aboutC. and falling within the general limits defined by the Points A-] ofthe appended drawing. These limits encompass cellulose ethers with ahydroxyethyl molar substitution (MS) of 1.0-3.5, a methoxyl degree ofsubstitution (D8) of 0.6-1.6, and a total degree of substitution (TDS)of l.4-2.4.

The terms molar substitution (MS) and degree of substitution (D8) areconventional terms describing substitution on the anhydroglucose unitsof the cellulose chain. The term total degree of substitution" (TDS)referers similarly to the average total number of cellulosic hydroxylgroups that are substituted per anhydroglucose unit. The total degree ofsubstitution will be less than the sum of the hydroxyethyl MS andmethoxyl DS because of formation of side chain glycol ethers.

In general, a high hydroxyethyl MS favors color compatibility, a lowermethoxyl DS gives a higher gel point, and a high total DS providesimproved enzyme resistance. The maximum possible total DS is 3.0.However, as indicated by Lindenfors (op. cit.), theoretically cellulosederivatives are not susceptible to microbiological attack if there is atleast one firmly bound substituent in every anhydroglucose. However, thefact that products with DS values over one are degraded enzymatically isindicative of the non-uniform substitution of the products. Also ahigher total DS is required for a product prepared from cotton lintersthan from a less crystalline wood cellulose.

Enzymes are chemicals secreted by fungi, bacteria and othermicroorganisms which split natural products into simple molecules whichthe microorganisms absorb for nourishment. Even in a sterile medium,enzymes can attack cellulose at points adjacent to unsubstitutedanhydroglucose units to form sugars. However, etherification greatlyincreases the resistance of the etherified unit to enzymatic attack.

The new ethers are prepared by reacting methyl chloride and ethyleneoxide with alkali cellulose at about 40-'60 C. The alkali cellulose isprepared by treating cellulose with about 1.2-3.0 moles of 35-70%aqueous NaOH per mole cellulose at about room temperature. A dip tank asdescribed in Savage U.S. Pat. 2,949,452, a spray mixer as described byErickson U.S. Pat. 2,469,764, or a slurry reactor as described byHaskins, e.g., U.S. Pat. 2,131,733 are suitable. Contact with air isminimized to reduce viscosity loss.

Etherification is carried out in a pressure reactor in the absence ofair at about 40-60 C. Because of the greater reactivity of the ethyleneoxide, the reactor is generally charged with the major proportion of themethyl chloride at room temperature, heated to about 40-50 C., and thenthe ethylene oxide added at a rate to maintain the desired temperature.However, incremental additions of methyl chloride and ethylene oxide canalso be used. Normally, a total of about 1.06.0 moles of methyl chlorideand about 3.4-7.0 moles of ethylene oxide are charged per mole ofcellulose.

Careful control of the exothermic etherification is necessary tominimize irregular and uneven substitution. To maintain a temperature ofabout 40-60 G, external cooling means are employed. Excess methylchloride can be used as a heat transfer and ebullient cooling agent.Other ebullient diluents such as dimethyl ether or a water-solubleorganic liquid such as isopropanol or tertiary butanol can also be usedto provide more effective heat transfer and moderate the rate ofetherification.

When the exothermic hydroxyethylation is completed, the reaction can befinished at 55-80 C. without harm. The overall reaction time may be 4-12hours. Then the reactor is vented, excess caustic is neutralized, andthe product purified by appropriate means.

Since the new hydroxyethyl methyl cellulose ethers are water-soluble butnon-thermal gelling below 100 C., the byproducts are removed by washingwith appropriate organic solvents or limited amounts of aqueous saltsolutions. Particularly useful in minimizing the loss of thewater-soluble product is the glyoxal insolubilization process describedin US. Pats. 3,347,847 and 3,527,751. After purification, the productcan be dried, granulated, ground, surface-treated, or otherwise preparedfor storage and end use. I

The new water-soluble hydroxyethyl methyl cellulose ethers exhibit manyof the properties of other watersoluble methyl cellulose ethers.However, they have a thermal gel point higher than about 100 C. They arereadily prepared in a wide range of viscosities. For use as a latexpaint thickener, a 2% aqueous solution viscosity at 20 C. of about400-100,000 cps. and preferably about 4,000-50,000 cps. is most useful.For other applications, products with viscosities lower than 400 cps.can be prepared as desired.

These cellulose ethers are particularly useful in aqueous latex coatingcompositions as thickeners and protective colloids for the dispersion offinely divided water-insoluble polymer particles. Examples of suchpolymeric materials are copolymers of monoethylenically unsaturatedcompounds such as styrene and acrylonitrile with a conjugated diolefinsuch as butadiene; homoand copolymers of styrene, acrylic andmethacrylic esters; vinyl halide and vinylidene halide monomers; andhomopolymers and copolymers of vinyl acetate. They can also be used witha carboxylic polymer latex such as described in Mesirov US. Pat.3,549,566.

Usually these latex coating compositions contain added pigment fillersand extenders such as titanium dioxide, barium sulfate, clays, mica,talc, silica, and the like. Particularly with colored pigments and dyes,the new hydroxyethyl methyl cellulose ethers provide superior colordevelopment as well as good film and application properties. Efiectiveresults are obtained using about 0.2-1.0 wt. percent HEMC, andpreferably about 0.25-0.6 wt. percent HEMC, based on total weight of theformulated paint.

The following examples illustrate further the present invention. Unlessindicated, all parts and percentages are by weight.

EXAMPLE 1 Preparation of HEMC (A) A pressure reactor was charged with250 parts (1.55 moles) of ground cotton linters, evacuated andrepressured with nitrogen several times. Then with internal agitationand blending, 356 parts (4.45 moles) of 50% aqueous NaOH Was sprayedonto the linters to prepare alkali cellulose. The reactor wasreevacuated, loaded with 400 parts (7.93 moles) of methyl chloride, andheated to about 44-50 C. Then ethylene oxide was added at a rate so that400 parts (5.87 moles) ethylene oxide were added in about 2.5-3.0 hourswhile maintaining a reaction temperature of about 44-50 C. Cooling wasprovided by cooling jacket and reflux of the low boiling reactants anddimethyl ether. After complete addition of the ethylene oxide, thereaction mass was heated at about 50 C. for another half hour beforecooling and venting the reactor.

To remove the water-soluble salts and byproducts, the crude solidproduct, about 1140 parts including about 380 parts HEMC, was blendedwith parts of 50% aqueous citric acid to adjust the pH to about 5.0followed by 24 parts of 40% aqueous glyoxal The mixture was blendedthoroughly and then heated at 70-90 C. for 20-30 minutes to obtain awater-resistant, surface crosslinking of the HEMC. The crude product wascooled to room temperature, washed twice by slurrying with about 6 partsof cold water per part of product and filtering, and then dried at80-120 C.

The purified HEMC (375 parts) was a white powder with a gel point of C.and a 2% aqueous solution viscosity of 35,300 cps. at 20 C. It had ahydroxyethyl MS of 1.73, a methoxyl D8 of 0.95, and a total of 1.76.* Itdispersed readily in water with gradual dissolution at an acid pH andrapid when basic. It had excellent salt compatibility, 100 parts of a 2%solution dissolving in separate tests 38 parts NaCl, 10 parts NaI-IPOmore than 50 parts sugar, 19 parts Na CO and 11 parts A1 (S0 3 beforesalting out. Its organic solubility in aqueous alcohol and acetone washigh. Also as shown below, its enzymatic resistance and compatibility instandard color development tests were both excellent.

(B) In another run 220 parts (1.23 moles) of ground cellulose pulp wastreated with 184 parts (2.3 moles) of 50% NaOH and then reacted with 78parts (1.54 moles) of methyl chloride at 50 C. for 2.5 hours. Theunreacted methyl chloride was vented and 20 parts of dimethyl etheradded. Then 360 parts (8.2 moles) of ethylene oxide was added over 2.5hours while holding a reaction temperature of 42-45 C. When theexothermic reaction ceased, the reactor was cooled and vented. Then 80pts. of 50% citric acid and 16 pts. of 40% glyoxal were sprayed onto thesolid reaction product and the mixture heated at 80 for 3 hours.

The glyoxal-treated product was washed with cold water and dried to givea purified HEMC having a gel point of 123 C., a 2% aqueous solutionviscosity of 15,600 cps. at 20 C., and a hydroxyethyl MS of 2.66, amethoxyl D5 of 0.70 and a total D8 of 1.54.

(C) A blender was charged with 175 parts (1.08 moles) of groundcellulose linters and sprayed with 240 parts (3.0 moles) of 50% NaOH inthe absence of air to form alkali cellulose. The alkali cellulose wastransferred to the etherification reactor and 280 parts (5.55 moles) ofmethyl chloride added. The reactor was heated to 42 C. and then 280parts (6.35 moles) of ethylene oxide was added over 2.5 hours as thetemperature was gradually raised to 48 C. Then the temperature wasincreased to 55 C. for 1.5 hours to complete the etherification.

The crude HEMC was purified as described in IA and IE to give a whitesolid with a gel point of 100 C., a 2% aqueous solution viscosity of29,700 cps. at 20 C., and a hydroxyethyl MS of 1.74, a methoxyl DS of1.12 and a total D8 of 1.71. Its enzyme resistance and colorcompatibility were excellent.

(D) In a similar manner 175 parts (1.08 moles) of ground cellulose wastreated with 260 parts (3.26 moles) of 50% NaOH and then reacted with100 parts (1.98 moles) of methyl chloride at 45 C. The reactor wasvented, parts dimethyl ether added, and at 42 C. 310 parts (7.0 moles)of ethylene oxide was added over The analyses are by conventionalmethods as described in ASTM D-1346-64 and D-2363-69. The hydroxyethylMS and methoxy US were determined by the modified Zeisel methoddescribed by Cobler, Samsel & Beaver, Talanta, 9', 473 (1962) usinghydriodic acid hydrolysis coupled with a gas phase chromatographicanalysis of the resulting mixed alkyl iodides. The hydroxyethyl DS wasdetermined by the modified phthalic anhydridapyridine method describedby Pascal, Comptes Rendus, 248, 225 (1959) and found to be specific forthe terminal primary OH of the hydroxyethyl ether group. The total DS isthen the sum of the methoxy] and hydroxyethyl DS. Gel points weredetermined using 1% aqueous solutions heated in a sealed arnpoule untilvisual phase separation.

The crude HEMC was purified by washing after glyoxal treatment to give awhite solid with a gel point of 115 C., a 2% aqueous solution viscosityof 80,00 cps. at 20 C., a hydroxyethyl MS of 1.53, a methoxyl D8 of 1.15and a total DS of 1.74. Its enzyme resistance and color compatibilitywere excellent.

(H) In other runs, cellulose was etherified with methyl chloride andethylene oxide using about 1.2-3.0 moles NaOH, 1.0-6.0 moles methylchloride, and 3.4-6.8 moles (E) A 3 gallon stirred reactor was chargedwith 600 ethylene oxide per mole of cellulose to obtain waterparts (3.71moles) of ground cellulose pulp. Air was soluble HEMC products withinthe area defined by Points removed by evacuating and repressurizing withnitrogen A-I in the accompanying figure. twice. Then the stirredcellulose was sprayed with 680 A detailed study of the HEMC analysesestablished parts of 50% NaOH (8.5 moles) added in about minananalytical variance (:38) of :L0.1 for hydroxyethyl utes. Then 250 parts(4.95 moles) methyl chloride was 15 MS, :0.06 for methoxyl DS, and 10.2for total DS. added. The reactor was heated to 42 C. and held 1 hourAlso revised analyses were found for several HEMC and then at 65 C. for45 minutes to achieve partial products:

Initial Revised HE (MS) MeO (DS) Total DS HE (MS) MeO (DS) Total DS 1.7a 0. 95 1. 76 2. 12550. 23 1. 14550. 06 1. 95550. 21 2. 66 0. 70 1. 542. 915:0. 09 0. 805;0. 04 1. 83550. 10 3. a4 0. 66 1. 92 a. 325:0. 05 0.61:1:0. 01 1. 87550. 21 1. 9s 0. 7s 1. 49 2. 3110. as 0. 835:0. 12 2.02:1:0. 23

methylation. After cooling to about C., 400 parts EXAMPLE 2 of dimethylether was added, the temperature adjusted to -45 C. and 600 parts (13.7moles) of ethylene oxide added in part increments every 20 minutes whilemaintaining a reaction temperature of about 45-50 C. The reactor washeld at C. for an hour after the ethylene oxide addition was completedbefore cooling and venting.

The crude HEMC was slurried with 90% acetone/ 10% H O, neutralized withglacial acetic acid, and then treated with 22 parts 40% aqueous glyoxaland 5.5 parts 50% aqueous citric acid per 1000 parts of crude HEMC. Theslurry was heated to 50 C., filtered hot and the solid product dried ina forced air drier at 80-120 C. The dried HEMC was further washed byslurrying with cold (10-20 C.) water, followed by filtration andredrying. The product was a water-dispersible powder with a gel pointhigher than 160 C., a 2% aqueous solution viscosity of 2810 cps. at 20C., and a hydroxyethyl MS of 1.37, a methoxyl DS of 0.53, and a total D8of 1.02. Its enzymatic resistance was poor.

(F) In another run, 600 parts (3.71 moles) of ground cellulose wassprayed at room temperature with 515 parts (4.50 moles) of 35% aqueousNaOH. The reactor was evacuated and 200 parts (3.96 moles) methylchloride and 200 parts dimethyl ether added. The mixture was heated to45 C. and 1016 parts (23.0 moles) ethylene oxide added over 3 hourswhile maintaining a reaction temperature of 45 "-50 C. After holding at50 C. for an hour after complete oxide addition, the reactor was cooled,vented, and dumped.

The crude product was slurried with aqueous acetone, treated withglyoxal at pH 3-5, and purified as described in Example 1E. The productwas a water-dispersible powder with a gel point higher than 160 C., a 2%aqueous solution viscosity of 3500 cps. at 20 C., and a hydroxyethyl MSof 3.34, a methoxyl D8 of 0.66, and a total D8 of 1.92. It had goodenzymatic resistance.

(G) Following the procedure of Example 1A, alkali cellulose preparedfrom 250 parts (1.55 moles) ground cellulose and 132.5 parts (3.30moles) sodium hydroxide was thoroughly blended with 400 parts (7.95moles) methyl chloride. The blended mixture was gradually heated to 56C. Addition of 300 parts (6.8 moles) ethylene oxidew as begun When thetemperature of the blended mass reached 45 C. and was completed in about1.7 hours while maintaining a temperature of about 56 C. After holdingat about 56 C. for an additional 0.5 hour, the etherification reactionwas finished by heating the mass at about C. for one hour.

HEMC as latex paint thickener The utility of the new HEMC products asthickeners for latex paint is illustrated by data obtained with standardlatex paint formulations and tests.

(A) Formulations Stock 3% aqueous solutions of the HEMC products wereprepared and used as the thickener solution in the following typicalexterior and interior latex paint formulations.

1.Exterior Acrylate Latex Paint Base Ingredients Lbs/100 gal. GallonsWater 124. 9 14. 99 Pigment dispersant (Daxad 3 8. 0 0. 96 Potassiumtripo1yphosphate 2. 0 0. 20 Defoamer (Polyglycol 1 -1200) 8.0 t 1. 08Preservative (Dowicil 100) 2.0 0. 17 Titanium dioxide, (Ti Pure R-9 200.0 6. 06 Calcium carbonate (Atornite) 257. 0 11. 37 Surfactant (TritonX-100) 5. 0 0. 57 Ethylene glycol 15. 0 1. 64 Acrylic latex (Rhoplex AC34)-... 387. 0 43. 50 3% Thickener solution 167. 0 20. 00

Total 1,175.0 10736 (2) INTERIOR POLYVINYL ACETATE LATEX PAINT BASEIngredients: Lbs./ 100 gal.

Water 300.0 Pigment dispersant (Daxad 30) 6.0 Potassium tripolyphosphate0.5 Surfactant (Igepal CO-630) 4.0 Preservative (Dowicil 100) 1.25Ethylene glycol 25.0 Titanium dioxide (Ti-Pure R-901) 250.0 Calciumcarbonate (Snowflake White) 100.0 Clay filler (ASP-400) 125.0 Coalescent(Texanol) 16.0 Polyvinyl Acetate Latex (Elvocit 1423) 250.0 Defoamer(Nopco NDW) 2.0 3% Thickener solution 167.0

1246.8 (B) Tests (1) Thickening efiiciency.The paint viscosity wasmeasured 24 hours after preparation. A viscosity of about -100 KrebUnits is normally desired with about 3-5 lbs. HEMC/ gal. of paint, i.e.,about 0.2-0.4 wt. percent HEMC based on formulated paint.

7 (2) Color development.--Paint samples are separately tinted withstandard colorants at room temperature and at 120 F. (49 C.). The heatedsample simulates tinting paint hot from a grinding step. Then 10 ml.draw-downs of the tinted paint samples are made on a Penopac comparedwith the hydroxypropyl methyl cellulose and improved enzymatic stabilitycompared with the hydroxyethyl cellulose. At the same time HEMC retainsgenerally equivalent thickening efficiency and flow and levelingproperties.

TABLE 1.HEMC AS LATEX PAINT THICKENER Enzyme stabJ Substitution Colordam vise. loss,

Gel Vise, KU Flow and 4 Wks.,

Latex paint Thlckener l 1 HE(MS) MeO(DS) Total DS point, 24 hrs. RT 120F. leveling percent Formulation 1, Exterior Aerylate-.- HPMC (1.0 HP) 0.9 70 4-. 4 5 HEC 2. 50 1. 00 100 2 25 HEMC-1A 1. 73 0. 95 1. 76 115 1042 2 4 2 HEMC-1C l. 74 1. l2 1. 77 100 103 2 2 4-5 6 HEMC-1F 3. 34 0.66 1. 89 160 93 2 3 2-3 9 HEMC-dH-l 2. 10 0. 97 1. 71 104 2 2 4 10HEMC-1D 1. 61 0. 88 1. 43 105 100 2 2 12 Formulation 2, Interior PVACHPMC (1 0 HP) 0. 9 70 80 2 4 0 HEMC-1B 2. 66 0. 70 1. 54 123 B2 2 4 5 15 lbs/100 gal; 0.43 wt. percent Formulation 1; 0.40 wt. percentFormulation 2 2 HPMC=Hydroxypropylmethyl cellulose (Methocel J 12 cules,Inc.).

a Blue "(3 Colorant (Hercules, 1110.).

0.5 p.p.m. Oellase 1000 enzyme.

HS, The Dow Chemical 00.). HEC =Hydroxyethyl cellulose (Natrosol 250 HR,Her- EXAMPLE 3 HEMC and color development Further data on the elfect ofHEMC substitution on color development with several different commercialpigments in the exterior acrylic latex paint Formulation 1 are given inTable 2.

TABLE 2-COLOR DEVELOPMENT TEST, 120F Rating 9 B Substitution Gel point,Vise Blue Thalo 0 Mon Viol Thlekener l HE (MS) MeO (DS) Total DS C K "0"Blue Black Red J 1. 73 0. 95 1. 76 115 104 2 2 2 2 2 2. 66 0. 70 1. 54123 77 2 3 2 3 2 1. 74 1. 12 1. 71 100 103 2 2 2 2 2 HENC-lfl-l- 2. 0.97 1. 71 100 104 2 2 2 2 2 i 5 lbs [100 gal 0 43 Wt. percent.

3 Scale: 1=Excel1ent, 10 =Very poor 8 Pigments: Blue C=Super ImperseBlue 0, Type X2688 (Hercules, Inc) Thalo Blue=Pthaloeyanine Blue (ColorCorp of America) 0 Black=0arbon Black (Hilton Davis). Mon Red=MonastralBed (Du Pont). V1olJ=Violet J Universal Colorant, Color Trend Series(California Ink Corp.).

using g. of latex paint applied to 2 ft. surface. The eifect of thethickener on flow and leveling is measured compared to standard brushouts with a rating of 1- best to l0-poorest.

(4) Enzyme stability-To evaluate enzyme stability or resistance, paintsamples are inoculated with a stand- EXAMPLE 4 HEMC and enzymeresistance Further data on the effect of HEMC substitution on the enzymeresistance of the exterior acrylate paint of Formulation 1 are given inTable 3.

TABLE 3.-ENZYME RESISTANCE 1 OF HEMC THICKENED ACRYLATE LATEX PAINTVise.

Substitution Gel Viscosity, KU loss,

point, 8 wks.,

Thiekener 1 3 HE(MS) MeO(lDS) Total DS deg. Init. 1 wk. 2 wks. 4 wks. 8wks. percent HPMC (1.0 HP) 0. 9 93 89 S3 83 83 11 HEC 2. 50 0 1. 00 10098 82 77 72 69 3O HEMC-1A 1. 73 0. 1. 76 104 103 102 100 99 5HEMC-1G" 1. 74 1. 12 1. 77 100 103 100 99 97 96 B HEMC-1H4- 2. 10 0.97 1. 71 103 97 95 92 9 HEMC-1H-2. 1. 96 0. 79 1. 49 160 87 83 82 83 7919 HEMC-1F 3. 3A 0. 66 1. 89 160 93 90 88 85 84 10 HEMC-1D--. 1. 61 0.88 l. 43 100 90 88 87 85 15 HEMC-1B 2. 66 0. 84 1. 54 123 86 77 78 77 7216 l 0.5 p. .m. Cellase 1000 enzyme. 1 5 lbs. 10!) gaL; 0.43 wt.percent.

I HPMC=Hydroxypropylmethyl cellulose (Methocel .T12HS) HEC=Hydroxyethylcellulose (Natrosol 250KB).

ard cellulose enzyme (Cellase 1000) and their viscosities areperiodically measured. The rate and total loss of viscosity are measuresof resistance to enzyme degradation.

(C) Results Typical results using HEMC to thicken the base latex paintformulation 1 and 2 above are given in Table 1. For comparison dataobtained concurrently with commercial hydroxypropyl methyl cellulose andhydroxyethyl cellulose thickeners are included. Note that the HEMCthickened paints have superior color development EXAMPLE 5 Modifiedlindenfors enzymatic stability test Apparatus and materials HaakeRotovisco Meter (Gebroder Haake K.G., West Berlin, Germany) with SV-lcup and bob for measuring viscosities of 400-70,000 cps. using a shearrate of 529 sec." at 582 r.p.m.

1.0% aqueous solution of the cellulose ether at pH 7.0:02.

1.0% aqueous solution of Cellase 1000 (cellulase enzyme, WallersteinCo., Deerfield, Ill.).

Method The cup of the Haake instrument is charged with 12 ml. of the 1%cellulose ether solution and assembled with the SV-l viscosity bob inthe thermostated jacket (2511" C.). The drive is engaged at 582 r.p.m.and the initial 1% viscosity read (Scale -100 units; 400-70,000 cps).The drive is disengaged, 1.2 ml. of the 1% Cellase 1000 solution added,and the drive re-engaged to measure the viscosity as a function of time.The viscosity loss is calculated based on the initial viscosity afteradding the cellulase enzyme.

Results Typical results are given in Table 4 and FIG. 2. Under the rapidhydrolysis conditions of the modified Lindenfors test, the celluloseether viscosity loss is essentially complete in 30 minutes. Theenzymatic stability measured by this test correlates well with the 4-8week accelerated paint stability tests of Examples 2-4. The HEMCproducts with a viscosity loss of less than about 60% in 30 minutes inthis test provide superior enzymatic stability when used as a latexpaint thickener.

Table 4 also includes color development test data obtained as describedin Example 2 using the exterior acrylate latex paint formulation andcommercial black, red and violet pigments. The combination of improvedenzymatic stability and pigment compatibility, as shown in the colordevelopment test, obtained with the HEMC products is a major advance.The new water-soluble, nongelling HEMC products are also useful in manyother applications as thickeners, protective colloids, soluble films,etc.

2. The water-soluble cellulose ether of claim 1 where the methoxyldegree of substitution is about 0.8-1.4 and the total degree ofsubstitution is about 1.6-2.1.

3. The water-soluble cellulose ether of claim 1 having 5 a 2% aqueoussolution viscosity of about 400-100,000

cps. at C.

4. The Water-soluble cellulose ether of claim I having a 2% aqueoussolution viscosity of about 4,000-50,000 cps. at 20 C.

5. The water-soluble cellulose ether of claim 1 further characterized bya -minute viscosity loss of less than about 60% as determined by themodified Lindenfors enzymatic stability test using a 1.0% solution ofthe cellulose ether and 10% cellulase enzyme based on the celluloseether at pH 70:02 and 25 C.

6. The water-soluble cellulose ether of claim 5 having a 2% aqueoussolution viscosity of at least 4,000 cps. at 20 C.

7. A process for preparing a water-soluble hydroxyethylmethyl cellulosehaving a thermal gel point greater than about 100 C., comprising:

(A) preparing an alkali cellulose by contacting cellulose with about1.2-3.0 moles of -70% aqueous NaOH per mole cellulose;

(B) blending the alkali cellulose with about 1.0-6.0

moles methyl chloride per mole cellulose and heating to about -50 C.;

(c) adding about 3.4-6.8 moles of ethylene oxide per mole cellulose overabout 2.5-4.0 hours while maintaining a temperature of about 40-60 C.;and thereafter (d) recovering a solid hydroxyethylmethyl cellulosehaving a hydroxyethyl molar substitution of about 1.0-3.5, a methoxyldegree of substitution of about 0.6-1.6, and a total degree ofsubstitution of about 1.4-2.4 as further defined in FIG. 1.

8. The process of claim 7 where after the ethylene 40 oxide addition,the reaction mixture is heated at about -80 C. for about 0.2-3.0 hrs.before recovering the solid hydroxyethyl methyl cellulose.

TABLE 4.MODIFIED LINDENFORS ENZYME STABILITY TEST Percent vise.

loss 2 Substitution Color Cellulose Gel 2% vlsc., dev., ether 1 HE (MS)MeO (DS) Total DS T, C. cps. 2 min. 30 min. 120 F.

HEC 2. 50 0 1.00 100 8, 000 73 4 [78/10 2/2/2 MC 0 1.8 1. 8 50 8, 000 69[88/10 10/10/10 HPMC-GEHG (0.15 HP) 1.8 1. 9 G5 4, 000 50 83 10/10/ 10HPMC-Jl2. (1.0 HP) 0.9 12,000 23 56 10/10/10 HPMC-J 75. (1.0 HP) 0. 975,000 38 70 10/10/10 HEMC-T 0. l3 1. 69 l. 82 6, 000 55 [(69/ 10)]10/10/10 HEMC-1A-1 2.12 1.14 1. 115 6, 000 13 46 HEMC-1G 1.53 1.15 1. 74115 80,000 14 40 2/3/2 HEMC-1H4 1. 09 1. 27 1. 81 84, 000 15 47 13/3/31HEMC-1H5 1. 33 l. 30 2. 08 124 24, 000 19 49 4/2/5 HEMC-llEI-fi... 1.491.35 2.10 95,000 13 38 4/2/5 HEMC-1H-7. l. 15 1.25 1. 96 106 56, 000 1750 3/2/5 HEMC-lH-8. 1. 27 1. 29 1.90 104 38, 000 5 24 4/3/ 6HEC=Hydroxyethyl cellulose (Nat-rosol 250 HR, Hercules). MC=Methylcellulose (Methocel MC, The Dow Chemical 00.). HPMC=Hydr0xypropymethylcellulose (The Dow Chemical 00.). HEMF-T=Hydmoxy'ethylmethyl cellulose(Tylose MH, Kalle AG).

2 Modified Lindenfors enzyme stability test.

Pigments, Aquablak (Cities serviceflMonastral Red (Du Pont)/Vlol'et 3'(Pittsburgh Plate Glass).

Percent loss in 10 minutes.

We claim:

1. A water-soluble hydroxyethylmethyl cellulose having a thermal gelpoint greater than about 100 C., a hydroxyethyl molar substitution ofabout 1.0-3.5, a methoxyl degree of substitution of about 0.6-1.6, and atotal degree of substitution of about 14-24 as further defined by FIG.1.

9. The process of claim 7 where the recovered cellulose 70 ether has a2% aqueous solution viscosity of about 400- 100,000 cps. at 20 C.

10. The process of claim 7 where the recovered cellulose ether has a30-minute viscosity loss of less than about 60% as determined by themodified Lindenfors 75 enzymatic stability test using a 1.0% solution ofthe cellulose enzyme based on the cellulose ether at pH 7.0:02. and 25C.

References Cited UNITED STATES PATENTS 5 10/1938 Haskins et a]. 260-1525/1949 :Erickson 260'-231 A 6/1958 Windover et al. 260--231 A 8/1958Swinehart et a1. 260-231 A 8/1960 Savage 260-231 A 1 10/1967Engelskirchen et a1. 260-232 6/1968 Rodgers et a1. 260-47 7/1969 Scherlf260-231 A 2/ 1970 12 3,527,751 9/1970 Gill 260-232 3,549,566 12/1970Mesirov 260-8 OTHER REFERENCES Lindenfors: Acta Chemica Scand., 16, pp.1111-1118, (1962).

Encyclopedia of Chemical Technology, vol. 3, pp. 496-7 and 510 (1965).

0 DONALD F. CZAJA, Primary Examiner R. W. GRIFFIN, Assistant ExaminerUS. Cl. X.R.

Greminger et a1. 106--170 15 106-170, 197 R; 117-166; 26017 R, 33.2 R

